A certain known X-ray CT device calculates an X-ray absorption coefficient (linear attenuation coefficient) from a projection image that is an X-ray transmission image of a test subject and captured from a plurality of directions, and acquires a reconstructed image that is a tomographic image of the test subject.
An integrated X-ray detector applied to such an X-ray CT device includes a plurality of detection elements, converts X-ray energy transmitted through the test subject to an electrical signal on an individual detection element basis, and acquires a projection image by outputting an integrated signal that has been integrated for a predetermined period of time. In this instance, the detection elements may include defective detection elements (hereinafter referred to as “defective elements”). The defective elements may shift a pixel sampling position, and thus alter an output value. As a result, artifacts may occur in the projection image.
Under the above circumstances, if a pixel defect occurs in a projection image due to a defective element, an imaging device described, for example, in Patent Literature 1 (PTL 1) estimates an output signal of the defective element from an output signal of a normal detection element, and corrects the influence exerted on elements surrounding the defective element by the defective element by using an influence quantity parameter that is predefined for the estimated value.
Meanwhile, an X-ray CT device having a photon-counting X-ray detector for measuring the number of X-ray photons has been developed in recent years. An X-ray CT device with a photon-counting X-ray detector is advantageous in being able to create an energy-specific pseudo-monochromatic reconstructed image, which cannot be acquired by an X-ray CT device having an integrated X-ray detector, and a reconstructed image of an absorption coefficient other than those indicating the distribution, for example, of atomic numbers (these images are hereinafter referred to as “multi-energy images”).
An embodiment of an X-ray CT device to which a photon-counting detector is applied allocates a plurality of minute detection elements to each pixel, measures the number of X-ray photons on an individual detection element basis, and adds up the resulting output values to determine the output of each pixel for a projection image. When the photon-counting detector is applied, a pile-up can be reduced in an X-ray CT device or other device using a very high X-ray dose rate. Further, reducing the size of the detection elements increases the number of detection elements used to capture an image of a particular area range. However, when the size is increased as needed at the photon-counting detector, that is, at the X-ray CT device in terms of the projection image, it is possible to suppress an increase, for example, in the amount of data to be processed by the X-ray CT device, the number of processing circuits, the number of processing steps, and the length of processing time.